17ß-estradiol protects against glucosamine-induced pancreatic ß-cell dysfunction.

OBJECTIVE: Glucosamine (GlcN) is a popular supplement for osteoarthritis in postmenopausal women. Although GlcN possibly induces insulin resistance, the effects of GlcN on ß-cell dysfunction are still obscure. METHODS: In the present study, we investigated changes in insulin production and ß-cell apoptosis in pancreatic islets after GlcN treatment in rats with or without ovariectomy and used MIN-6 cells to investigate the protective effects and molecular mechanisms of 17ß-estradiol (E2) in GlcN-induced ß-cell dysfunction. The rats were divided into four groups: (1) sham operation (SHAM; n = 8); (2) SHAM with 750 mg/kg/day GlcN injected intraperitoneally for 14 days (SHAM + GlcN; n = 10); (3) ovariectomy (OVX; n = 9); and (4) OVX with 750 mg/kg/day GlcN injected intraperitoneally for 14 days (OVX + GlcN; n = 9). RESULTS: Both GlcN and ovariectomy reduced the expression of insulin, determined by the staining intensity of insulin and reverse polymerase chain reaction. GlcN alone also induced ß-cell apoptosis, and this adverse effect was aggravated after ovariectomy. In addition, we found that GlcN decreased calcium influx and insulin secretion by decreasing the protein levels of inwardly rectifying potassium in the ATP-sensitive potassium channel. GlcN decreased the protein levels of endoplasmic reticulum (ER) stress-associated proteins, including C/EBP homologous protein, phospho-protein kinase-like endoplasmic reticulum kinase, phospho-eukaryotic initiation factor 2α, and phospho-c-Jun N-terminal kinase. Finally, GlcN decreased cell viability. E2 counteracted GlcN-mediated attenuation in intracellular calcium concentration, extracellular insulin secretion, protein levels of inwardly rectifying potassium, cell viability, and protein levels of ER stress-associated proteins. ICI182.780 inhibited these beneficial effects of E2. CONCLUSIONS: GlcN impairs insulin secretion of ß-cells by inhibiting Ca influx and enhancing ß-cell apoptosis with increases in ER stress-related proteins, whereas E2 counters these adverse effects of GlcN.